Marketable Securities - Unrestricted Marketable Securities-Unrealized Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014 investment	Dec. 31, 2013 investment
Schedule of Available-for-sale Securities [Line Items]
Total number in loss position (investments)	2	1
Less than twelve months - fair values	$ 17,449	$ 12,460
Less than twelve months - unrealized losses	(93)	(229)
Twelve months or greater - fair values	0	0
Twelve months or greater - unrealized losses	0	0
Total Fair Value	17,449	12,460
Total Unrealized Losses	(93)	(229)
Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total number in loss position (investments)	2	1
Less than twelve months - fair values	17,449	12,460
Less than twelve months - unrealized losses	(93)	(229)
Twelve months or greater - fair values	0	0
Twelve months or greater - unrealized losses	0	0
Total Fair Value	17,449	12,460
Total Unrealized Losses	$ (93)	$ (229)
Unrestricted Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments with other than temporary impairments (investments)	0